The use of plastic cards such as credit cards or bank cards for performing, e.g., financial transactions, is becoming increasingly popular. As is well known, a conventional plastic card including a magnetic card can't store a large quantity of data and has a problem in security. As semiconductor technology has been remarkably developed, the size of integrated circuits (ICs) have become increasingly reduced. Consequently, plastic cards having an IC chip (called “a smart card”) have been developed to replace the conventional magnetic card. The smart card can store a very large quantity of data and has advantages such as enhanced security and durability. Accordingly, the smart card has been used for various purposes such as an identification card, a health insurance card, and a bank card.
Since important data such as a credit card number, a resident registration number, a bank account number, and a password are stored in the IC of a smart card, security with respect to the data stored in the IC is very important.
FIG. 1 is a diagram of an exemplary IC for a smart card. An IC 10 in the smart card includes a central processing unit (CPU) or a processor 11 such as a microprocessor, a random access memory (RAM) 13, a read only memory (ROM) 14, an electrically erasable and programmable ROM (EEPROM) 15, and an input/output controller 12. The circuit blocks in the IC 10 are connected to one another through a system BUS 16, thereby transmitting and receiving data, programs, and controlling codes.
Those who are skilled in the art related to an IC can easily distinguish circuit blocks from a system BUS and monitor data loaded on the system BUS by using a predetermined means. If data transmitted and received among the circuit blocks is exposed to a hacker and abused, a serious social problem will be occurred.
Thus, it is highly desirable for a smart card which is used as a credit card, a health insurance card, and an identification card to have functions capable of retaining security of data transmitted and received among internal circuit blocks.